diff --git a/internal/agent/agent.go b/internal/agent/agent.go
index 31d311a..e72cee5 100644
--- a/internal/agent/agent.go
+++ b/internal/agent/agent.go
@@ -1545,24 +1545,33 @@ func (a *Agent) reportCompute(ctx context.Context, out chan<- *llmgwv1.AgentMess
 }
 
 // memBandwidth is the node's memory read rate in GB/s, 0 until measured.
-// Measured once a process, in the background, the first time it is asked
-// for: it reads half a gigabyte, which must not hold up an agent reaching
-// its control plane, and the heartbeat carries it when it is known. Once a
-// process rather than an agent, so tests running many agents in one read it
-// once.
+// Measured in the background, the first time it is asked for: it reads half
+// a gigabyte, which must not hold up an agent reaching its control plane,
+// and the heartbeat carries it when it is known. Not at once but after a
+// minute or so, chosen at random, and again every hour, keeping the best:
+// VMs on one host that all restart together measure each other, and read a
+// third less than any of them gets alone. Once a process rather than an
+// agent, so tests running many agents in one read it once.
 func (a *Agent) memBandwidth() float64 {
 	bwOnce.Do(func() {
 		go func() {
-			bw := measureBandwidth()
-			bwBits.Store(math.Float64bits(bw))
-			if bw > 0 {
-				a.log.Info("this node's memory", "read_gbs", math.Round(bw*10)/10)
+			time.Sleep(bandwidthDelay())
+			for {
+				if bw := measureBandwidth(); bw > math.Float64frombits(bwBits.Load()) {
+					bwBits.Store(math.Float64bits(bw))
+					a.log.Info("this node's memory", "read_gbs", math.Round(bw*10)/10)
+				}
+				time.Sleep(time.Hour)
 			}
 		}()
 	})
 	return math.Float64frombits(bwBits.Load())
 }
 
+// bandwidthDelay is how long an agent waits before measuring, so agents
+// started together measure apart.
+var bandwidthDelay = func() time.Duration { return 10*time.Second + rand.N(110*time.Second) }
+
 var (
 	bwOnce sync.Once
 	bwBits atomic.Uint64
diff --git a/internal/agent/main_test.go b/internal/agent/main_test.go
index 76842a1..1e62bbe 100644
--- a/internal/agent/main_test.go
+++ b/internal/agent/main_test.go
@@ -3,11 +3,13 @@ package agent
 import (
 	"os"
 	"testing"
+	"time"
 )
 
 func TestMain(m *testing.M) {
 	// Half a gigabyte read per test binary, and contending with the tests
 	// for the CPUs: these never look at the figure.
 	measureBandwidth = func() float64 { return 0 }
+	bandwidthDelay = func() time.Duration { return 0 }
 	os.Exit(m.Run())
 }